Vocal learning in songbirds is a unique, experimentally accessible model of human vocal learning that also exemplifies the general process of motor learning using sensory feedback. A male songbird learns his courtship song by first memorizing his father's song, and later using auditory feedback to match his own song to his memory of his father's song. One major advantage to this model system is the existence of separate forebrain circuits involved in producing the song and in learning it. The so-called "anterior forebrain pathway", which is essential for vocal learning, has recently been found to bear gross similarities to the mammalian basal ganglia pathway, which is known to be involved in motor control and motor learning. Specifically, the general circuit connectivity, neurotransmitters used, and neuron classes present, are consistent with the hypothesis that the same basic circuitry underlies information processing in avian and mammalian basal ganglia. The experiments proposed here will use electrophysiological and morphological approaches to test whether key microcircuitry of the anterior forebrain pathway supports this view. In addition, the experiments will test whether neuromodulatory actions of dopamine in the anterior forebrain pathway are similar to those in mammals. These experiments will provide necessary information about how the avian anterior forebrain pathway works. If the hypotheses are supported, two major benefits will ensue. First, work on the avian song system will accelerate because it can be guided by the wealth of information already available for mammals. Moreover, the song system, with its advantages of a well-studied, naturally-learned behavior, will be validated as a more directly applicable model system of mammalian basal ganglia function than heretofore realized. Such complementary approaches to understanding the basal ganglia are valuable because approaches to disorders of the basal ganglia such as Parkinson's and Huntington's diseases will likely require fundamental understanding of information processing in the basal ganglia. [unreadable] [unreadable]